Best value pump for a 5L roto

I’m putting together a 5L on the uber cheap. I found a used polysci chiller, a referbed 5L, and now I’m trying to figre out what pump I should get. Normally, I would do a Welch DryFast, but I was wondering if I could do it cheaper.

Anyone got some good suggestions for a pump on the cheap for this guy?

New or used, don’t care.

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I use my faucet vs a chiller for my 5l rotovap. Or a pond pump/bucket/ice water works.

As far as pump, ebay welch wob-l diaphram! Cheap, and no worry of oil containment.


I just found a welch 2090b on ebay a few days ago for amazing cheap. That’s the SUPER SIZE version of the Welch Dryfast from a few years ago. I figure if it doesn’t work I get my money back and at around 150$ shipped for 88 L/Min @ 29" hg it will save me some vacuum oil!

Oh there were 2 listed when I found mine.

Still one left:

I run harbor freight pumps with cold traps and a regulator. Super cheap and last long enough


I always prefer chemical duty diaphragm pumps. I get tired of dealing with oil, as I have to do that enough with the short path.

I get tired of filling dry ice into cold traps too.


I always prefer better equipment also. I was focusing on the word cheap. Dealing with oil sucks ill be getting a diaphragm soon too I hope. I use my harvest right freeze dryer as a cold trap.

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I’m trying to not spend another 3200 for a brand new DryFast Ultra pump. Looking for alternatives. $800 for a Welch Wob-l pump looks very intresting.

I can not find any real info on the Welch 2090B-01

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A humbolt aspirator pump allows me to boil etoh at 44C. Not sure what kind of vacuum I’m pulling (no guage), but you could probably pull a deeper vac using mineral oil instead of water. I also have it connected to a 4.3 GPM cheap $14 water pump, while it should be attached to something in the 7-9 GPM range. Idk if it would work on a roto, but it works great on my little vacuum still.

I found a catalog that listed it:

I found it before from a vendor and saved it/changed the name and now I can only find it on this scribd thing. It shows how killer it is though compared to the other dryfast pumps and it does use the same numbering pattern (20 for chemical duty and the next two numbers are close to the L/Min). It is the only one that uses 3/8" instead of 1/4". I bet it was expensive.

I paid 100 to 200 shipped for my welch wob-l 2585b pumps used in good condition on eBay. the 2581 is an identical pump with lower cfm but pulls a deeper vacuum I haven’t seen those for cheap on eBay yet. Mind you I’m a cheap bastard so 200 dollars or more is high dollar for me ha

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I use a wob-l 2522b for my 5l roto with out any issues. It only pulls to -25hg, but I read -13 to -15hg is only really needed. I scored 2 for $198.00 each off Ebay. I use them for Buchner filtration as well. No cold trap used


Ebay has vaccubrand md1c diaphragm pumps you can offer down to around 700 buck usually. I’ve gotten three of them that way. 1.5 mbar


Is the Welch 2522B-01 chemical resistant? I’d like to be able to use it for ethanol recovery and DCVC with heptane, but I’m not sure if it will handle heptane very well. I was looking at the PILOT economy pump that Beaker has linked to, but the ability to pick up a used Welch for half the price of the PILOT is pretty enticing. Not if I’m constantly having to rebuild the damn thing or use cold traps, though. I’m guessing the Welch doesn’t have all of the teflon coatings?

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get a diaphragm pump its the best for rotovaps


My welch eats cda12 fine

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What are your guys opinion on this diaphragm pump?

I’m planning on using it with a 50l rotovap and wondering if I should go for their YH700 instead that’s a little stronger.

So I have the 2090b up and running. It is amazing! No oil and according to my old gauge it pulls close to 30" HG. It is so fast it makes the air filter whistle. I’m still waiting for a few fittings to get it all proper but I’m using it to purge right now and it is easily 4x faster than using my old pump.

The thing is massive, though and I built a big stand and used 3/4" rubber washers but it walked the stand around I had to bunjee the stand down.

They are chemical duty btw…


I was looking at those a few weeks ago and thought it would be overkill for my application. I might be rethinking getting one after that review.

I’m pretty sure its overkill for anything. It moves a lot of air and it has the highest vacuum rating I’ve seen on a chemical duty diaphragm pump.

Who makes the 2090B?